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Taxonomy, Evolution, Pal Indicators TAXONOMY, EVOLUTION, BIOGEOGRAPHY AND PALAEOENVIRONMENTAL SIGNIFICANCE OF VICTORIAN PALEOGENE OSTRACODA Col Eglington Department of Earth and Planetary Sciences Faculty of Science Macquarie University Sydney This thesis is submitted to fulfil the requirements for the degree of Doctor of Philosophy from Macquarie University. All results and interpretations in this thesis are the original work of the author except where acknowledged in the customary manner. No part of this work has been submitted previously for a higher degree to any other university or institution. Col Eglington AUGUST, 2014 Department of Earth and Planetary Sciences Faculty of Science Macquarie University Sydney ii ABSTRACT Section 1. The Otway Basin of southeastern Australia, which formed as part of the Australo-Antarctic Gulf during separation of Australia and Antarctica, provided a congenial marine environment for Ostracoda (Crustacea) to flourish and diversify during the Cenozoic era. Ostracod genera and species evolved rapidly and were limited ecologically by depths and temperatures. The combination of rapid rates of evolution and high ecological sensitivity makes assemblages of these morphologically complex microscopic crustaceans highly useful as biostratigraphic and especially palaeoecologic tools. Balancing evolutionary and ecologic aspects, however, requires caution in making judgements about biostratigraphic implications of specific assemblages. Their biostratigraphic value is increased when considered in conjunction with foraminiferal associations, often the principal basis for making stratigraphic alignments. Though Cenozoic strata are widespread in western Victoria, they are generally masked by extensive Plio-Pleistocene lava sheets and are relatively rare in outcrop. Much information has been gained from the vast number of water and petroleum bores drilled through the basaltic cover into the Cenozoic sequences beneath, but relatively little of the vast amount of cores and cuttings has been subjected to palaeontologic study; none of the Paleogene intervals had previously been investigated for ostracods. The seven subsurface (from bores) and surface sections on which this study is based, are all located within the Otway Basin. Section 2. In Latrobe-1 bore, 22 samples from a 137 m interval, ranging in age from the Paleocene–Eocene boundary to Early Eocene produced 23 taxa from nine families; two species are new: Neobuntonia taylori sp. nov. and Tasmanocypris? latrobensis sp. nov. Because of insufficient material, 14 other taxa discussed are presented in open nomenclature. The study extends the time and geographic range of most of the genera and species obtained. Section 3. Early Eocene ostracod assemblages from the Rivernook Member of the Dilwyn Formation (Wangerrip Group) were obtained from two locations: one an outcrop, the other subsurface in Latrobe-1 bore. Samples from these sites yielded 33 taxa of which 24 were reinvestigated. Two new “dwarf” varieties, Neonesidea australis var. A and Glencoeleberis? thomsoni var. A, are proposed. Due to marked differences in faunal composition of each of the three substantial Rivernook outcrop assemblages, they could not be bulked together and treated as a single assemblage. Assemblages from the Pember Mudstone, Rivernook and Princetown members, and the Trochocyathus and Turritella beds provided data for palaeoenvironmental interpretation. Assemblage comparisons revealed a high degree of commonality between the Rivernook Member (RMA) and Pebble Point, the South Australian Late Eocene, and Late Eocene New Zealand assemblages. There was a very low degree of commonality when compared with an Eocene Antarctic assemblage. The only other bore to provide Late Paleocene/earliest Eocene ostracods, Heywood-10, had a very small latest Paleocene assemblage in the Pember Mudstone of the Dilwyn Formation. Ostracods from the Rivernook outcrop and Heywood-10 bore are the first from those locations. Section 4. A small group of Cytherella with non-typical valve overlaps (LV>RV) is endemic to the Australian and New Zealand region. Descendants of C. atypica Bate (1972), the ancestral form from the Western Australian Late Cretaceous, migrated into the Australo- Antarctic Gulf. Cytherella postatypica sp. nov., a direct descendant, is found in the Otway Basin from the Late Paleocene to Middle Miocene. It is very similar in appearance to C. pinnata McKenzie et al. (1993), a species with a normal (RV>LV) overlap. Conspecificity was considered but rejected because of small, consistent differences in size, outline in lateral iii view, extent of overlap, central muscle scars, and shape of juveniles. Cytherella batei sp. nov. and six taxa in open nomenclature are all new left-valve-dominant Cytherella from various Otway Basin localities that range in age from Late Eocene to Early Miocene. Inversacytherella Swanson et al. (2005), erected to accommodate Cytherella with reversed valve overlap, but otherwise morphologically very close to Cytherella postatypica and C. pinnata, and the discovery of C. conturba sp. nov., an Oligocene species in which both left- dominant and right-dominant overlaps are found, are viewed as evidence for invalidity of that supposed new genus. Section 5. Early Eocene (Ypresian) ostracod assemblages are used for palaeoenvironmental interpretations at four locations in the northeastern part of the Australo- Antarctic Gulf. A controversial hypothesis for estimating benthic O2 levels using two ostracod groups, the platycopids and podocopids is applied to samples from bore and outcrop sections of the Pebble Point and Dilwyn formations (Wangerrip Group). In order to assess the validityt of the technique the results are compared to the foraminiferal data and presence of other ostracod taxa. It was found to concur in six instances, was contradicted in two and ambiguous in three, its veracity could not be definitively decided. Palaeoenvironmental interpretations based on ostracod and foraminiferan assemblages are presented. There was a high degree of variability in ventilation of the substrate, despite the generally highly restricted conditions existing in this broad shelf area of the Australo- Antarctic Gulf. The environment for the Late Paleocene Pebble Point Formation outcrop assemblage was cool and well-oxygenated, deeper than the younger Rivernook Member of the Dilwyn Formation. The very small Late Paleocene Pember Mudstone (Dilwyn Formation) assemblage from Heywood-10 bore survived in a warm, shallow, poorly-oxygenated, marginal marine location. Conditions were uniformly warm and shallow for the Early Eocene Dilwyn Formation locations, but the range of estimated benthic O2 from very low to very high, and variations in composition of the assemblages, illustrate the instability of local conditions in different strata of this marginal marine setting. Section 6. An Early Oligocene marine ostracod assemblage from the Narrawaturk Formation of the Nirranda Group occurs subsurface in the Heywood-10 bore. The sampled assemblage includes 32 taxa in 19 genera from 10 families. Two species and one subspecies are new; eight other taxa are reviewed in further detail, and eight kept in open nomenclature. The new taxa are Aversovalva hasta sp. nov., Xestoleberis heywoodensis sp. nov. and Oculocytheropteron ayressi Majoran, 1997 varius subsp. nov. The assemblage diversity was measured using the reciprocal of Simpson's Diversity Index. The Narrawaturk Formation assemblage had a lower level of diversity and abundance than the Late Oligocene Gellibrand Marl from the same locality, but a higher degree of diversity than an Early Oligocene assemblage from the Port Willunga Formation of South Australia. There was a very low level of commonality between the Narrawaturk Formation compared with the Victorian Oligocene Angahook Member. The assemblage characteristics indicate a well-ventilated inner-shelf environment with some degree of transportation. Although Australian Oligocene Ostracoda have been described from the Eocene/Oligocene boundary in South Australia, from Willunga Embayment cores, and from outcrops in the Aire and Torquay districts of southern Victoria, these specimens are the first described from the Narrawaturk Formation. Section 7. A Late Oligocene marine ostracod assemblage from the Gellibrand Marl of the Nirranda Group occurs subsurface in the Heywood-10 bore. The sampled assemblage includes 53 taxa from 33 genera across 17 families. Twenty-five taxa were reviewed and 21 placed in open nomenclature. The diverse assemblage indicates that this inner-shelf location was slightly deeper and farther from shore than the Early Oligocene Narrawaturk Formation iv from the same location. The water was warm, shallow and well-oxygenated. Previous Gellibrand Marl ostracod assemblages have been of Miocene age; these specimens are the first described from the subsurface Oligocene Gellibrand Marl. Section 8. Glencoeleberis? thomsoni Hornibrook (1952), found in and above the latest Paleocene/earliest Eocene Pember Mudstone Member, Early Eocene Rivernook Member, and in Late Paleocene/Early Eocene dredged marine sediments from Fiordland in the South Island, New Zealand, provides evidence for an early breach of the Tasmanian land-bridge connecting Australia and Antarctica. Previous work suggested that breaching of the land bridge closing the eastern end of the Australo-Antarctic Gulf (that had prevented through- flow into the Tasman Sea) commenced in the mid-Late Eocene. The extension in distribution of this otherwise exclusively regional
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